1. Field of the Invention
The invention relates to a high frequency welding installation for welding particularly plastics material parts, as used, for example, for manufacturing bathtub liners or motor vehicle mats.
2. Description of the Invention
Different types of high frequency welding installations are already known. For example, installations with a sliding table composed predominantly of a work station and one or two feed stations are available on the market. These installations include so-called trays which, provided with the workpiece or with component parts of the workpiece, are pushed from the respective feed station into the work station. After the welding procedure has been carried out, the tray is again pushed from the work station into one of the feed stations. Simultaneously, an already loaded tray can be pushed from the second feed station into the work station. Thus, in the known installation, conveying takes place, for example, from the first feed station into the work station and again back into the first feed station, without a continuous conveying in a single conveying direction being possible. Depending upon the number of feed stations, this known installation requires for its operation at least two or four operators, with only one work station being provided in each case. Accordingly, this known installation is labor intensive. In addition, this installation is usually not expandable in a modular manner as desired, so that it is not possible to have the first and single work step, namely the welding step, be followed by other work steps. For example, if two feed stations are present in one work station, two working places must be provided including the necessary accessories, for example, deposits for finished and unfinished material. This again requires a relatively large amount of space.
In addition, high frequency welding installations in the form of round tables or revolving tables are known. These installations consist essentially of a round table or a revolving table which has at its periphery several receptacles for the workpieces, wherein the number of receptacles corresponds to the number of the provided work or operating stations. Such a revolving table usually has four tables or workpiece receptacles which rotate jointly about an axis. The width required for this installation is very large since it requires at least the width of three tables. The operation of the tables or the feeding of the workpiece receptacles is possible only from one of the long sides of the respective tables. In addition, it is not possible to deposit material in a manner conforming to the working steps and an operation by means of manipulating devices (robots) is not provided. Moreover, the known revolving table arrangement cannot be expanded indefinitely because the number of stations is already fixed from the conception of the arrangement. Additional work stations cannot subsequently be inserted. Also, these rounded tables always have the same cycle times. Thus, depending upon the cycle time, always only a relatively short cooling time is available, so that a sufficient cooling time cannot be provided, for example, when welding with closed cover tools is performed. Only the entire cycle time can be adjusted to the length of the cooling time. This, in turn, reduces the efficiency of the arrangement. In these known revolving table arrangements, the transport speed can be increased only to a limited extent because of the existing centrifugal forces. This is because if the transport speeds are increased, the parts to be welded together, which are exactly placed relative to each other in the feed station, are cast from their positions.
Finally, high-frequency welding installations are known in which a continuous, linear conveyance of the workpieces to be welded is possible through the successively arranged stations. These installations are either equipped with transport chains which have at their top side drive means for the plastic sheets to be welded, as described in German Offenlegungsschrift No. 33 12 418, or they have receiving trays for the parts to be welded together, wherein the receiving trays are fixedly fastened to the transport system. The finished workpiece must be removed from the transport system at the end of the work portion or feed portion thereof, because the workpieces would fall or tilt from the transport receptacles or trays during transition to the next transport system portions (vertical or parallel portions located underneath). Accordingly, it is not possible to return the trays with the welded parts thereon to the initial station. In addition, at least twice the number of trays must be provided than the corresponding number of stations because at least as many unloaded trays as loaded trays are in circulation. In these known installations, a fixed cycle time is also used in all portions of the transport device. Thus, it is not possible to have the trays returned more quickly or to have the trays stay for a longer time in a cooling station.
It is the object of the invention to provide a high-frequency installation which is relatively simple and additionally very flexible in its structure and very economical.